It is known to carbothermally reduce oxidic boron raw materials in a low-shaft electric arc furnace whose electrodes reach toward the furnace bottom from above and are of adjustable height so that close to the furnace bottom, upon which a melt of the alloy is formed, a reducing zone is constituted into which the electrodes extend. The burden or charge above this reducing zone consists of fine-grained boron-containing raw material, fine-grained oxides of the basic metal and/or small pieces of the basic metal as well as carbon carriers. Above the reducing zone, this charge or burden is constituted as a gas-permeable burden layer.
The term "fine-grained" as used herein with reference to the oxides and carbon, refer to a more or less pulverulent material with a particle size up to about 5 mm.
The term "small pieces" with reference to the basic metal, means pieces with a maximum dimension in any direction ranging from 5 to 100 mm and of any shape.
In general, the electrodes are raised and lowered in accordance with the conductivity of the burden, usually with an automatic control system.
Finally, as to general matters, it should be noted that all percentage values given herein, unless indicated otherwise, represent percentage by weight.
Boron alloys consisting of boron, a basic metal and unavoidable impurities of associated elements have been produced heretofore mainly by aluminothermal techniques. By way of example, one can refer to the earlier method of producing ferroboron, described in Durrer/Volkert, "Metallurgie der Ferrolegierungen" (Metallurgy of Ferroalloys) 1972, pages 689,690. In these processes, the oxidic boron raw material and iron oxide are reduced with aluminum and melted. The product is an aluminum-containing ferroboron of, for example, 5 to 16% boron up to 4% aluminum, a maximum of 1% silicon, a maximum of 3.10% carbon, balance iron and unavoidable impurities. It is also possible to produce ferroboron of, for example, 18 to 20% boron up to 2% aluminum, a maximum of 2% silicon, a maximum of 0.1% carbon, balance iron and unavoidable impurities. While aluminum and silicon can be considered impurities as well, the amounts of these impurities have been given because they ar substantially greater than other common impurities and generally unlike other impurities have an effect upon the properties of the product.
For example, for the production of metallic glasses using ferroboron, the aluminum content thereof is exceptionally disadvantageous because the aluminum easily oxidizes and the resulting oxides can block the nozzles which are used to produce the metallic glasses. Similar disadvantages characterize other hitherto known boron alloys when these are employed as master alloys for the production of amorphous metal alloys.
In the last decade, developments have progressed in the field of amorphous metal alloy production, i.e. the production of alloys of transition metal with metalloids.
When an amorphous structure was desired, generally it was necessary to cool at high speed a molten steam of the low melting composition.
The amorphous metal alloys can be divided into the iron-based alloys, the cobalt-based alloys, the nickel-based alloys, molybdenum-based alloys and other alloys.
Predominantly for the iron- and/or nickel- and/or cobalt-based amorphous metal alloys, the metalloid has been boron. For practically all technologically important amorphous metal alloys, aluminum is a detrimental element. For this reason it has been sought to produce boron-containing master alloys that are practically aluminum free. However, boron alloys were produced by prior art techniques predominantly involving aluminothermal methods and thus could not avoid having a more or less high content of aluminum.
It is, therefore, desirable to make boron alloys of a basic metal which is free from or practically free from, aluminum.
It is a goal of this invention to provide a method of making a cobalt-based boron alloy and/or nickel-based boron alloy which is practically aluminum free, the term "and/or" used here indicating that a single alloy can be formed of boron where the base metal consists of both cobalt and nickel.
It has been proposed to reduce oxidic boron-containing raw materials to produce boron which forms a boron alloy with a basic metal and unavoidable impurities using carbothermal techniques, especially for the production of ferroboron alloys Durrer/Volkert, (op. cit. page 689).
In this case, the burden or charge consists of a carbon carrier in fine-grained form, for example milled coal and milled coke. Generally, the gas permeability of the burden layer here requires that this layer have a height well below 500 mm. The carbon carrier, if wet, may not adequately dry in such layer. The method results in a ferroboron alloy or a ferroboron silicon alloy which is practically free from the detrimental aluminum and can have an aluminum content as low as 0.07%. However, a drawback of this system is the fact that the boron content of the alloy is also comparatively low. The yield is unsatisfactory. In the production of ferroboron alloys by this approach, the boron content can be only about 10% while in the production of ferroboron silicon alloys, the boron content is reduced to about 3% while the silicon content is also about 3%.
Indeed, these problems are not solved when the burden mixture is initially put up as large-particle pellets and a higher charge or burden height is provided in the furnace with the pelletized burden.
Tests have shown that practically the same results are obtained when there is used a cobalt-based boron alloy is used as a nickel based boron alloy.